1. Field of the Invention
The invention relates in general to a flexible sheet explosive and, more particularly, to a thermally stable sheet explosive which is relatively insensitive to impact and shock and which can be used to cut and/or deform an object without exposing the object to excessive heat or detonation pulse.
2. Description of Related Art
Sheet explosives have been used extensively in civilian applications in demolition, industrial, and experimental work. The sheet explosives consist of coarse grade of pentaerythritol tetranitrate (PETN) and an energetic binder containing nitrocellulose and a plasticizer. The explosive output of the sheet explosive is controlled to a certain extent by varying both the explosive solids loading of PETN and by adding more powerful explosives, such as cyclotrimethylene trinitramine (RDX) and cyclohexamethylene hexanitramine (HMX), to the PETN-based formulation. These sheet explosives are considered unsatisfactory for use in some applications because they lack both thermal stability and impact insensitivity, since PETN is inherently sensitive to initiation by heat, impact, and shock. Attempts to develop a thermally stable and shock insensitive replacement for PETN have thus far been unsuccessful.
Through extensive testing, it has been found that current heat-resistance explosives, such as HMX, hexanitrostilbene, nonanitroterphenyl, bispicrylaminodinitropyridine, and octanitroterphenyl, simply lack the low critical thickness required to be used in detonable thin sections when combined with an appropriate amount of inert elastomeric binder to obtain a flexible sheet. Approximately 40% (60% explosives solids loading) of inert elastomeric binder is required to form a flexible sheet with the above-described explosives, but in the case of HMX, in some thicknesses, at least 90% solids loading is required to obtain a detonable material. Formulations with 90% solids are mechanically rigid in nature and tend to have very high detonation pressures. It appears that the critical thickness criteria can only be achieved by increasing the explosives solids loading at the expense of decreased flexibility and low detonation pressures.
It is, therefore, desirable to have a flexible sheet explosive that is thermally stable at temperatures approaching 150.degree. C. and which is relatively insensitive to impact and shock.
Additionally, it is desirable to provide a flexible sheet explosive having a selectively adjustable explosive output.
It is also desirable to have a flexible sheet explosive which solves the problem of flexibility and excessive detonation pressures.